For example, Patent Literature 1 discloses an optical disk reproduction apparatus that involves error correction, and this optical disk reproduction apparatus issues a warning to the user according to the condition of the information recording surface of the optical disk.
Patent Literature 1 determines the availability of error correction of the reproduced data or counts the number of symbols that executed the correction, estimates the condition of the information recording surface of the optical disk according to the count result, and thereby warns the user. As a result of using Patent Literature 1, the user is able to accurately learn of an optical disk with inferior recording quality, and take measures such as backing up the data.
Moreover, for example, Patent Literature 2 discloses an optical disk reproduction apparatus for reading, from an optical disk, main information such as contents information as well as identifying information (sub information) requiring integral detection, and this optical disk reproduction apparatus reproduces sub information in which unauthorized duplication is difficult.
According to Patent Literature 2, the main information such as contents information is recorded with a recording mark, and the identifying information required for the reproduction of the main information is recorded by displacing the edge of the recording mark in the track direction. The optical disk reproduction apparatus of Patent Literature 2 generates a correlation signal based on the M series, extracts the displacement direction of the recording mark edge, and performs integration by associating the displacement direction of the recording mark edge with the M series. It is thereby possible to reproduce identifying information which is impossible to copy or reproduce under normal circumstances, and realize the copyright protection of the main information.
Moreover, for example, Patent Literature 3 discloses an optical disk reproduction apparatus capable of stably and accurately reading second digital information as the copyright protection information without being influenced by defects and pit fallouts existing on a disk-shaped recording medium.
In Patent Literature 3, with respect to the second digital information that is recorded by wobbling the pit sequence that is recorded as a first signal on the disk-shaped recording medium, a plurality of bits configuring the second digital information is sorted and recorded in unit intervals of the same synchronizing signal contained in the foregoing first signal. Subsequently, the plurality of bits configuring the second digital information recorded as described above are read a plurality of times for each of the unit intervals of the synchronizing signal during the reproduction, and information of the foregoing bits that were read is integrated. It is thereby possible to integrate information from the numerous wobbling pits across the unit intervals of a plurality of synchronizing signals, and determine the value of the respective bits.
Moreover, for example, Patent Literature 4 discloses an optical disk reproduction apparatus capable of shortening the processing time while maintaining a predetermined accuracy regarding the detection of additional information recorded on an optical disk based on the slight displacement of pits.
In Patent Literature 4, the optical disk reproduction apparatus comprises a detection circuit for detecting a push-pull signal, and an integration circuit for integrating the push-pull signal and detecting the additional information by performing binarization processing to the integrated result. Moreover, this optical disk reproduction apparatus additionally comprises a control circuit for controlling the total number of frames to be used for creating valid additional information in the integration circuit. The control of this control circuit is performed based on the error correction result in the error correction circuit.
Nevertheless, the foregoing conventional optical disk reproduction apparatuses are not equipped with a function for controlling the timing of implementing the error correction in the integration detection of the sub information that has been subjected to error correction encoding. Moreover, in the integral detection, the detection accuracy of the sub information will increase as the integral width becomes longer. Nevertheless, if the error correction processing is implemented in a state where the integration interval is short and the detection accuracy of the sub information is extremely inferior, the error correction effect is minimal, and there is a problem that the probability of so-called erroneous correction of correcting the wrong code will increase.
For example, the optical disk reproduction apparatus of Patent Literature 1 estimates the recording condition of the optical disk based on the error correction result, and, to begin with, does not perform integral detection. Thus, Patent Literature 1 does not disclose controlling the timing of implementing the error correction.
Moreover, although Patent Literatures 2 and 3 disclose the integral detection of the sub information, they do not disclose controlling the timing of implementing the error correction of the sub information that has been subjected to error correction encoding.
Moreover, although Patent Literature 4 determines whether to continue the integration based on the error correction result of the integral detection, the size of the integral value, and the variation of the integral value, it does not disclose controlling the timing of starting the error correction.